Long-Term Effects of Logging on African Primate Communities: a 28-Year Comparison From Kibale National Park, Uganda

If logging is to be compatible with primate conservation, primate populations must be expected to recover from the disturbance and eventually return to their former densities. Surveys conducted over 28 years were used to quantify the long-term effects of both lowand high-intensity selective logging on the density of the five common primates in Kibale National Park, Uganda. The most dramatic exception to the expectation that primate populations will recover following logging was that group densities of Cercopithecus mitis and C. ascanius in the heavily logged area continued to decline decades after logging. Procolobus tephrosceles populations were recovering in the heavily logged areas, but the rate of increase appeared to be slow (0.005 groups/km 2 per year). Colobus guereza appeared to do well in some disturbed habitats and were found at higher group densities in the logged areas than in the unlogged area. There was no evidence of an increase in Lophocebus albigena group density in the heavily logged area since the time of logging, and there was a tendency for its population to be lower in heavily logged areas than in lightly logged areas. In contrast to the findings from the heavily logged area, none of the species were found at a lower group density in the lightly logged area than in the unlogged area, and group densities in this area were not changing at a statistically significant rate. The results of our study suggest that, in this region, low-intensity selective logging could be one component of conservation plans for primates; high-intensity logging, however, which is typical of most logging operations throughout Africa, is incompatible with primate conservation. Efectos de Largo Plaza de la Tala en Comunidades de Primates Africanos: Una Comparación de 28 Años en el Parque Nacional Kibale, Uganda Resumen: Si se espera que la tala sea compatible con la conservación de primates, se deberá esperar que las poblaciones de primates se recuperen de las perturbaciones y que eventualmente retornen a sus densidades previas. Utilizamos estimaciones llevadas a cabo a lo largo de 28 años para cuantificar los efectos a largo plazo de la tala selectiva tanto de baja como de alta intensidad en la densidad de los cinco primates comunes presentes en el Parque Nacional Kibale, Uganda. La mas dramática excepción a las expectativas de que las poblaciones de primates se recuperarían posteriormente a la tala fue el hecho de que las densidades de grupos de Cercopithecus mitis y C. ascanius en un área fuertemente talada continúan disminuyendo aún décadas después fuertemente taladas; sin embargo, la tasa de incremento parece ser lenta (0.005 grupos/km 2 por año). Colobus guereza aparenta estar bien en ciertos hábitats perturbados y fuéron encontrados en mas altas Paper submitted December 17, 1998; revised manuscript accepted May 26, 1999. 208 Selective Logging and Primate Conservation Chapman et al. Conservation Biology Volume 14, No. 1, February 2000 densidades de grupo en las áreas taladas que en las áreas no taladas. No hubo evidencia de un incremento en densidades de grupo de Lophocebus albigena en las áreas altamente taladas a partir del tiempo de tala y se observó una tendencia en la densidad de sus poblaciones a ser más baja en áreas fuertemente taladas que en las áreas ligeramente taladas. En contraste con los resultados de las áreas altamente taladas, ninguna de las especies presentó densidades de grupo más bajas en las zonas ligeramente taladas que en las zonas sin tala, y las densidades de grupo en esta área no cambiaron a una tasa estadísticamente significativa. Los resultados de este estudio sugieren que en esta región la tala selectiva de baja intensidad podría ser un componente de los planes de conservación para primates; sin embargo, la tala de alta intensidad, que es típica en la mayoría de las operaciones de tala a lo largo de Africa, es incompatible con la conservación de primates. saker (1976) documented that it was nearly 10 years after the loss of approximately 90% of a major food resource that a statistically significant decline in vervet monkeys ( Cercopithecus aethiops ) at Amboseli, Kenya, could be detected. Most other studies have not had data on primate abundance from before and after logging and thus use neighboring unlogged sites to compare with the logged site (but see Grieser-Johns & Grieser-Johns 1995). This approach cannot take into account natural variation in primate abundance within undisturbed forest ( Johns 1986; Chapman & Chapman 1999). The generalizations that can be drawn from investigations of the effects of logging are limited because primate densities at the study sites are affected by confounding factors such as hunting (Mittermeier & Coimbra-Filho 1977; Wilkie et al. 1992, 1998; Oates 1996; Struhsaker 1997; Rosenbaum et al. 1998). Furthermore, few of these studies examine the effects of more than one intensity of logging on the primate community in question (but see Struhsaker 1975, 1997; Skorupa 1988). Studies examining the effects of variable intensities of logging over several decades, preferably with data collection before and after logging, are needed for researchers to discern how selective logging affects primate populations. Our objective was to examine the long-term effects of selective logging on density of the five most common diurnal primate species of Kibale National Park, Uganda. To meet this objective, censuses were conducted over 28 years to (1) compare primate group densities between unlogged, lightly logged, and heavily logged areas and (2) evaluate the recovery of primate populations following logging. Most logging regimes call for some sort of rotation: the area is logged, left to recover for a specified period, often 30–50 years, and logged again. We suggest that if logged areas are to be compatible with primate conservation, primate populations must recover from the initial disturbance and return to their former densities over a period of time shorter than the typical period between logging rotations. Our investigation proposes explanations for similarities and differences in primate densities between unlogged, lightly logged, and heavily logged sites and suggests sustainable logging practices at Kibale and other similar forests. Introduction Although they cover only 6% of Earth’s arable surface, tropical forests account for nearly 50% of all known species (National Research Council 1992). The future of these highly diverse ecosystems is threatened by escalating rates of forest conversion and degradation ( Johns & Skorupa 1987; Struhsaker 1987; Brown & Lugo 1990). Less than 5% of tropical forests are legally protected from human exploitation, and many of these legally protected areas are subjected to illegal exploitation (Redford 1992; Oates 1996; Chapman & Onderdonk 1998; Chapman et al. 1999 a ). Furthermore, many tropical species are locally endemic or are rare and patchily distributed (Struhsaker 1975; Richards 1996). Such restricted distributions predispose many tropical forest species to an increased risk of extinction when habitats are modified (Terborgh 1992) because national parks and reserves, even if effectively protected, cannot conserve species whose ranges do not fall within a protected area. As a result, conservation of many tropical forest species depends on the capacity of disturbed forests to support their populations. Because all forms of extractive exploitation result in biological loss and ecosystem change, knowledge of how particular species are affected by extraction and an understanding of their speed of recovery from disturbance are essential for developing sound conservation and management plans for disturbed forest habitats. The most prevalent form of disturbed forest habitat with conservation potential is selectively logged forest (Skorupa 1988; Frumhoff 1995; Struhsaker 1997). Although a number of studies have examined the effects of selective logging on primate populations, the majority have been limited by methodological shortcomings. Some studies have been conducted soon after logging has occurred (Plumptre & Reynolds 1994; Bennett & Dahaban 1995; Ganzhorn 1995; Rao & van Schaik 1997) and may be inappropriate for examining the effect of logging on primate communities because habitat modification often lowers recruitment but does not usually kill primates (Struhsaker 1997). Thus, in many cases, declines in primate populations become evident only years after logging (Skorupa 1988). For example, Struh-